1. Field of the Invention
The present invention relates to a photo printer in which an image is thermally formed on a sheet of roll paper and the image is fixed by irradiation with light of a prescribed wavelength. More specifically, the present invention relates to a roll paper feeding device of the photo printer.
2. Description of the Background Art
A photo printer employing roll paper includes a roll paper feeding device holding and feeding the roll paper, an image forming device forming an image by heating a sheet of roll paper fed from the roll paper feeding device at a prescribed temperature, an image fixing device irradiating the sheet of roll paper on which the image has been formed with ultraviolet ray to fix the image, and a cutting device cutting the sheet of roll paper on which the image has been fixed to a prescribes size to finish a photograph. In such a photo printer, roll paper is consumed as photographs are printed, and the diameter of the roll becomes smaller. Therefore, the roll paper feeding device of a conventional photo printer has such a structure as shown in FIG. 5.
FIG. 5 is a schematic diagram representing a structure of a main portion of a conventional roll paper feeding device.
As shown in FIG. 5, the conventional roll paper feeding device includes a paper feed roller 4, a holder 5, a pressing lever 6, and a sensor 8 reading information printed on a side surface of roll paper 100. The information printed on the side surface of roll paper 100 represents the type of roll paper (for example, whether it is for color printing or mono-tone printing), and based on the information, the photo printer controls various components described above.
Holder 5 is provided with an L-shaped slit 50 consisting of a vertical slit 50a and a horizontal slit 50b. Holder 5 supports a shaft 71 of a supporter 7 supporting roll paper 100, with the shaft 71 of supporter 7 axially supporting roll paper 100 being inserted through vertical slit 50a and fit into horizontal slit 50b. Shaft 71 is pressed by pressing lever 6 toward paper feed roller 4, so that supporter 7 moves toward paper feed roller 4 and roll paper 100 comes to be in contact with paper feed roller 4. Further, as holder 5 has horizontal slit 50b as a part of L-shaped slit 50, even when shaft 71 is pressed by pressing lever 6, the shaft abuts the inner wall of horizontal slit 50b, and therefore, the shaft is not raised but held movable in a prescribed direction.
A plurality of other photo printers have been proposed that include such a roll paper feeding device holding the roll paper movable in a prescribed direction (for example, in Japanese Patent Laying-Open Nos. 2002-308482, 2002-347302 and 2002-347999).
In the conventional roll paper feeding device 1 such as shown in FIG. 5, pressing fever 6 must continuously press shaft 71 of supporter 7, until fully wound roll paper 100, axially supported by supporter 7, is completely used up. For this purpose, the center of rotation of pressing lever 6 is arranged as close as possible to paper feed roller 4. It is noted, however, that sensor 8 must be mounted between the center of rotation and paper feed roller 4. Because of this positional limitation, a small sensor 8 must be used. Sensor 8 is simply for reading bar-code information printed on a side surface of roll paper 100. Therefore, considering the performance, a larger sensor, which is less expensive than a smaller one, may be used. Use of such a large sensor, however, was impossible because of the positional limitation mentioned above.
When shaft 71 of supporter 7 is mounted to slit 50, pressing lever 6 must once rotate in a direction away from paper feed roller 4. Therefore, the center of rotation of pressing lever 6 is arranged closer to paper feed roller 4 than the center line of vertical slit 50a. When the center of rotation of pressing lever 6 exists near the center line, it follows that the fulcrum (center of rotation), point of action (tip end) and point of force for rotating pressing lever 6 are approximately aligned in the vertical direction, and hence, for rotation, supporter 7 must be pushed with large force. This makes it difficult to load supporter 7.
When supporter 7 is to be removed from L-shaped slit 50, pressing lever 6 is detached abruptly from shaft 71 and is turned quickly back to the initial position, as the object receiving the pressing force by rotation of lever 6 is lost. This causes a large bang, and may cause damage to pressing lever 6.